Presser foot mechanisms



P 13, 1966 J. R. IOANNILLI ETAL 3,272,162

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United States Patent 3,272,162 PRESSER FOUT MECHANISMS .IosephR. Ioannilli, Beverly, and Roger E. Lemay, West Peabody, Mass, assignors to United Shoe Machinery Corporation, Boston, Mass, a corporation of New Jersey Filed Apr. 23, 1964, Ser. No. 361,961 Claims. (Cl. l1261) The present invention relates generally to improvements in shoe outsole sewing machines or stitchers and, more particularly, to presser foot mechanisms to provide improved gripping of work pieces in such machines.

While stitching shoe outsoles of varying thicknesses to shoes, particularly at high speeds, with onventional machines two serious problems are encountered in presser foot operation with resultant adverse effects upon the stitch forming functions of the machine. The first problem is a tendency of the presser foot to bounce upwardly after being brought into contact with the work. This upward bounce results from the fact that the presser foot is being urged toward the work by a light tension spring, the force of which is drastically reduced in operating upon thin work pieces. As a result of the light spring pressure the presser foot tends to bounce away from the work piece before the presser foot is locked in place. Since the amount of thread measured for the formation of each stitch in an outsole sewing machine is determined by the locked height of the presser foot above the work support presser foot bounce results in measuring excess thread for the work thickness.

The second difiiculty encountered in conventional outsole stitchers is that of changes in presser foot forces accompanying changes in work thickness. Generally as the work thickness increases the presser foot spring is extended and the force of the presser foot correspondingly increased. This increased force is particularly objectionable, however, since thick soles are frequently of a relatively soft, yielding rubber or crepe and the added force of the presser foot tends to interfere with the free motion of the thread in the work piece.

It is accordingly an object of the present invention to provide a shoe outsole sewing machine in which the presser foot exerts a uniform force upon the work piece under varying work thickness conditions.

Another object of the invention is to prevent bouncing of the presser foot away from the work.

A further object of the invention is to improve the accuracy of needle thread measurement in shoe outsole sewing machines particularly while these machines are operating at high speeds.

Still another object is to regulate accurately the compressing force of the presser foot upon the work piece.

In the achievement of the foregoing objects one of the novel features of the invention relates to the provision of a torsion spring for lowering the presser foo-t into contact with the work when the presser foot lock is released. The force exerted by the presser foot is regulated by winding the spring through a hand knob readily accessible on the front of the machine. In order to maintain uniformity of presser foot force under conditions of changing work thickness the torsion spring is coupled to the presser foot through connections which include, according to another feature of the invention, a force compensating cam connected to the torsion spring by a steel tape. The cam is mounted on a shaft, the angular position of which varies in accordance with workpiece thickness and the shape of the cam is such that it provides a shorter input arm to the shaft and thus compensates for increases in spring torque corresponding to increased work thickness. The result is that the torsional force at the shaft and the clamping force at the presser foot 3,272,162 Patented Sept. 13, 1966 remain constant over the entire range of Work thicknesses for which the machine is designed.

The foregoing objects and features of the invention will be more fully appreciated and understood from the accompanying detailed description of an illustrative embodiment taken in connection with the accompanying drawings in which:

FIG. 1 is a view in right side elevation of a portion of a shoe outsole sewing machine including a presser foot spring and connections according to the present invention;

FIG. 2 is a schemati illustration of the presser foot spring of FIG. 1 while the machine is operating on work of maximum thickness;

FIG. 3 is a graph showing compensation for variations in presser foot spring torque as a result of changes in work thickness;

FIG. 4 is a view partly in section along the line IVIV of FIG. 1 and showing the presser foot spring and some of its associated connections;

FIG. 5 is a fragmentary view showing some of the parts depicted in FIG. 1 while the machine is operating upon a work piece of maximum thickness;

FIG. 6 is a view similar to FIG. 5 but showing the machine operating on a work piece of minimum thickness; and

FIG. 7 is a view similar to FIG. 2 showing the presser foot spring while the machine is operating upon work of minimum thickness.

Referring now to the drawings, the machine embodying the present invention includes, in addition to a presser foot 10, a work support 12 which cooperates with the presser foot for clamping and feeding the work as in conventional shoe outsole sewing machines. There is also included a curved hook needle 14, a curved work piercing awl 16, a looper 18 for placing the thread in the barb of the needle and a thread hook 20 for storing needle thread to be given up as the needle withdraws from the Work piece. In addition the Work piece, which comprises a welt 22 and outsole 24, is guided by an edge gauge 26 to locate the seam at a uniform predetermined distance from the sole edge about most of the periphery of the shoe.

The timing of presser foot motions corresponds generally to those of prior machines. Its operation to grip and release the work is effected through a presser foot lock of conventional construction indicated generally at 28 in FIGS. 1 and 6. The presser foot 10 is secured by screws 30 to the forward end of a presser foot lever 32, pivoted on a fixed axle 34 and pivotally connected at 36 to the upper end of a vertical link 38. There is interposed between the lock 28 and the link 38 a floating lever 40 to the central portion of which the lower end of the link is pivotally connected at 42. The floating lever 40 is pivotally connected at 44 to a vertical slide 46 of the lock 28 which also includes a case 48 con taining a series of staggered rolls 50 for gripping and releasing the slide 46. The case 48 is fixedly supported upon a portion of the main frame 52 of the machine.

For driving the various stitch forming and work clamping instrumentalities of the machine including the presser foot there is provided a cam shaft 54 journalled in the frame 52 and rotated one revolution for each complete stitch forming cycle. A cam 56 is keyed to the shaft 54 and a bell crank 58 pivoted on a shaft 60 is actuated by the cam for imparting a work compressing and releasing motion to the presser foot 10. At the distal end of one of its arms the bell crank carries a follower roll 62 which engages a track 64 in the cam 56 and the other arm of the bell crank is slotted at 66 to provide an adjustable pivotal connection at 68 to the upper end of a vertical link 70. The lower end of the link 70 is pivotally connected at 72 to the forward end of the floating lever 40.

It will be appreciated from the foregoing description of presser foot operating connections of conventional design, that during a part of each operating cycle a uniform oscillating motion is imparted to the presser foot to clamp and release the work. However, the starting point of the clamping motion as derived from the same track 64 varies in accordance with the position of the pivot 44 which in turn is determined by the thickness of the work piece. The extent of cam-derived presser foot motion is varied by the position of the pivot 68 in the slot 66: closer to the shaft for less motion and farther from the shaft 60 for greater motion.

For moving the pivot 44 to the starting level of the work clamping stroke there is provided according to a feature of the invention, a torsion spring 74 having an adjusting end terminating in a loop 76 and an output end terminating in a hook 78. The spring 74 is wound loosely around a retainer 80 secured to a boss on the inside of the frame 52 by a screw 84 and a nut 85 (FIG. 4). For adjusting the torque of the spring 74, there is a headed adjusting screw 86 (FIG. 1) passing through the loop 76 and threaded into an appropriate tapped opening in a boss formed integral with the frame 52. At its forward end the screw 86 is provided with a hand knob 88 for the convenience of the operator in adjusting the force exerted by the spring 74.

The force of the spring 74 is transmitted in a controlled manner to the presser foot 10 through connections which include the slide 46. A pivot 90 connects the lower end of the slide 46 to a short link 92, the other end of which is pivotally connected at 94 to the forward end of a generally horizontal lever 96. At its rearward end the lever 96, which is pivoted on a fixed axle 98, is slotted at to receive an adjustable pivotal connection in the form of a shoulder screw 102 which couples the lever 96 to a generally vertical link 104. The upper end of the link 104 is connected by a pivot 106 to an arm 108 pinned to a rockshaft 110. The connections just described are such that a torsional force applied in a clockwise direction to the shaft 110 while the lock 28 is released causes the slide 46 to rise and the presser foot to be lowered into contact with the work. The position of the shoulder screw 102 in the slot 100 adjusts the amount of torque transmitted from the shaft 110 for lowering the presser foot 10 into engagement with the work: farthest from the axle 98 for greatest presser foot force.

For imparting the torsional force to the shaft 110 there is keyed to the shaft 110 a torque compensating arm or cam 112 having a curved peripheral slot into which is fitted a steel tape 114. The forward end of the tape 114 is anchored by a screw 116 to the forward face of the arm 112. The rearward end of the tape 114 has secured to it an adapter 118 including an eye which is slipped over the hook 78 of the tension spring 74. The shape of the curve on the arm 112 in contact with the tape 114 is such that it compensates for changes in the torsional force of the spring 74 to maintain a constant force at the shaft 110 as will hereinafter be explained in greater detail.

When the machine is stopped at the end of a seam, the presser foot is raised through a set of connections which overcome the spring 74 and impart the required motion to the shaft 110. These connections include a slotted link 120 into the slot of which is loosely received a pin 122 fitted into the distal end of a short arm 124 extending outwardly from a hub of the cam 112. The link 120 is pivoted at 126 to a lever 128 which is free to turn on a stopping rocks-haft 130 journalled in the frame 52 at the rear of the machine. The effective length of the link 120 is adjustable by means of a threaded connection between the slotted part and that part in Which the pivot 126 is located. A check nut 132 is provided to lock the threaded connection 125 in place when the desired length has been attained. During normal operation of the machine the pin 122 travels freely in the slot on the link 120 without affecting the shaft 110.

In stopping the machine, however, the shaft is rocked in a counterclockwise direction as seen in FIG. 1 and, after the presser foot lock 28 has been released, causes a set screw 136 threaded in an upstanding arm 138 secured to the shaft, to engage the lever 128 causing it also to turn in a counterclockwise direction. The turning of the lever 128 on the shaft 130 brings the distal end of the slot in the link 120 into engagement with the pin 122 and continued motion is imparted as a counterclockwise rocking of the shaft 120. Since the lock 128 is released at this time, the slide 46 slides downwardly and the floating lever 40 pivots about the pin 72 to raise the presser foot 10.

The presser foot lock 28 of the present machine is of generally conventional design and is locked and released by conventional instrumentalities only partially illustrated in FIG. 1. These operating instrumentalities comprise a lever 140 pivoted on a fixed axle 142 mounted in a pair of integral upstanding ears of the case 48. The lever 140 has a vertically extending arm pivotally connected at 144 to a horizontal rod 146 around which is wrapped a compression spring 148. The rod 146 projects forwardly beyond the pivot 144 and the forward end of the rod is engaged by conventional instrumentalities and pressed rearwardly against the spring 148 which is compressed between a shoulder on the rod and a stationary abutment 0n the frame 52. Under the force of the spring 148 a short downwardly extending arm of the lever 140 presses on the uppermost of the rolls 50 to apply a gripping force to the slide 46.

On stopping of the machine conventional mechanism associated with the rockshaft 130 is effective for pulling the rod 146 rearwardly to release the lock before the shaft 110 is rocked in a counterclockwise direction to raise the presser foot. The rod 146 is pressed rearwardly during a part of each operating cycle of the machine by a cam actuated lever pivoted on the shaft 60 and having a depending arm 150 into the lower end of which a set screw 152 is threaded and locked by a check nut 154. The screw 152 is adjusted in the arm 150 to engage the forward end of the rod 146 and urge it rearwardly to release the lock 28 for a brief period. During this time interval the force of the spring 74 causes the presser foot 10 to be lowered into engagement with the work. After the slide 46 is again locked by the rolls 50, the presser foot is further depressed to squeeze the work by.the shape of the cam track 64 which imparts a descending motion to the link 70 against a fixed position of the pivot 44. The cam track 64 is also formed to cause the raising of the presser foot during a portion of each sewing cycle while the work support 12 is being back fed in preparation for another work advancing motion.

In order to prevent damage to the presser foot 10 or to the work support 12 when the presser foot is lowered in the absence of a work piece, a stop has been provided comprising a button 156 pressed into a depending portion of the arm 124. There is threaded in a portion of the frame 52 (not shown) a set screw 158, which is abutted by the button 156, to limit the clockwise motion of the shaft 150 in order to arrest the downward movement of the presser foot 10 at a level above the work support 12 The spring 74 is formed to include an angle D (FIG. 2) of 70 between the loop 76 land the end of the hook 78 while in its free or unstressed state. As installed in the machine the spring 74 has imparted to it a minimum torsional stress or pre-load of 30 thereby resulting in a minimum operating angle D of 100. The operating range of work thicknesses results in an additional torsional stress of 45 being imposed upon the spring 74 between the minimum and maximum work thicknesses for which the machine is intended. This corresponds to a work thickness range from approximately /s" to A and the torque output of the spring as shown in FIG. 3 increases from 47 lb.-inches when the angle D is equal to 100 to 117 lb.-inches when the angle D equals 145, the ratio of maximum spring torque to minimum spring torque being 2 /2:1. If the full torque of the spring 74 were applied to the shaft 110 the result would be that through the connections already described, the thickest work piece would be pressed against the work support v12 under a presser foot force 2 /2 times that applied to a work piece of minimum thickness. Difiiculties would accordingly be encountered in work feeding, in thread measurement and in the movement of the thread in being positioned in an excessively compressed yielding material as already indicated. It is possible that in operating on work pieces of uniform thickness the torque of the spring 74 could be partially adjusted through the knob 88 to minimize these difficulties. However, such adjustments are a practical impossibility when operating upon a work piece of tapered or varying thickness.

In order to maintain relatively constant presser foot force throughout the work thickness range of the machine the varying torque of the spring 74 is translated by the cam 112 to a substantially uniform torque at the shaft 110. The shape of the cam 112 is such that regardless of torque output T of the spring 74 the torque T at the shaft 110 remains substantially uniform at 60 lb.- inches as indicated by the dotted line in FIG. 3 which represents the torque relationship over the range of 100- 145 of the angle D. In addition to changes in the torque output T of the spring 74 it is necessary, in order to obtain absolutely constant torque at the shaft 110, to correct also for a change in the angle B which is defined between the tape 114 and a line 162 normal to a radial line of the spring 74 passing through its point of attachment to the tape. As seen in FIGS. 2 and 7 the angle B is equal to approximately 30 when the langle D is at its maximum, i.e. 145". As work thickness and the angle D are reduced the angle B is also reduced to zero and then increases to a value of perhaps 5 in a clockwise direction from the tape 114 as shown in FIG. 7. Under the conditions depicted in FIG. 2 the force acting in the direction of the tape 114 is equal to the total force along the line 162 multiplied by the cosine of 30 e.g. F =F (cos 30) a maximum correction of approximately 13.4%. This necessary correction however, can be further reduced by designing the spring 74 with an angle D such that the zero point for the angle B occurs at the center of the operating range. If this is done the angle B reaches a magnitude of 17.5 on each side of the tape 114 and the reduction in force from the line 162 to the tape 114 is accordingly less than 5% as shown above. A minor correction may be introduced in the form of a cam .112 to compensate for changes in the angle B.

The major correction introduced by the cam 112, however, is for the change in torque T of the spring 74 to obtain a uniform torque T equal to 60 lb.-inches at the shaft 110 for the variations in the angle D of 100-145 This is accomplished by reducing an effective moment arm M (FIG. 2) about the shaft 110 to which the force of the spring 74 is applied, in accordance with the increase in the torque T of the spring. Thus, the value of M for any condition of spring torque T in order to maintain a constant torque T of 60 lb.-inches at the shaft 110 is given by the equation:

in which R is the length of the moment arm of the spring 74. When the value of R is taken as 1" which is convenient in the present case, the value of M equal 1.28" for a value of 47 lb.-inches corresponding to a value of 100 for the angle D, obtained while operating on work of minimum thickness. At the other extreme of the opcrating range when the value of T reaches 117 lb.-inches at for angle D while operating on work of maximum thickness, the value of M equals .51".

If it is desired to correct for the angle B, the value of this angle of approximately 5 depicted in FIG. 7 produces a negligible correction in the value of M. For correcting the value of M when the \angle B equ als approximately 30 the value of M previously obtained is divided by the cosine of 30 and yields a corrected value of .59". From the foregoing data a shape for the cam 1 12 is derived by conventional analytical methods to provide a torque T having adequate uniformity for all practical purposes.

From the foregoing it will be apparent that the present invention may be readily modified for applications other than those in presser foot mechanisms of sewing machines. It will also be obvious that certain of the parts may be changed in character without departing from the spirit of the invention. For example, a chain or cable may be substituted for the flexible tape 114 so long as the substituted connection is sufficiently flexible to contact the surface of the cam and has suificient tensile strength and fatigue characteristics to afford reasonable durability for its intended environment. It is accordingly not intended that the foregoing illustration should be taken by way of limitation of the invention but rather that the scope of the invention be interpreted in terms of the appended claims.

Having thus described our invention what we claim as new and desire to secure by Letters Patent of the United States is:

1. A sewing machine comprising a curved hook needle, a work support upon which a work piece having a thickness within a predetermined range of work thicknesses is supported while being penetrated by the needle, a presser foot for gripping the work piece against the work support, a torsion spring producing a torque output proportional to work thickness, a lock releasable during a portion of each sewing cycle for permitting the presser foot to be urged toward the work support under a force from the spring and interconnecting means for translating the torque output of the spring into a relatively constant force applied to the presser foot throughout the range of work piece thickness.

2. A sewing machine comprising a curved hook needle, a work support upon which a work piece having a thickness within a predetermined range of work thicknesses is supported while being penetrated by the needle, a presser foot for gripping the work piece against the work support, a torsion spring producing a variable torque output increasing in proportion to work thickness, a presser foot lock including a movable element releasable to permit the presser foot to be resiliently urged toward the work support during a portion of each sewing cycle, a rockshaft connected to the movable element and compensating means on the rockshaft to which the variable torque output of the torsion spring is connected to provide a relatively constant force for urging the presser foot toward the work support regardless of work thickness.

3. A sewing machine comprising a curved hook needle, a work support upon which a work piece having a thickness within a predetermined range of work thicknesses is supported while being penetrated by the needle, a presser foot for gripping the work piece against the work support, a torsion spring producing a variable torque output increasing in proportion to work thickness, a presser foot lock including a movable element releasable to permit the presser foot to be resiliently urged toward the work support during a portion of each sewing cycle, a rockshaft connected to the movable element, a flexible link connected to the spring, and means including a cam fixed to the shaft and to which the other end of the flexible link is connected to compensate for the variable torque output of the spring.

4. A sewing machine comprising a curved hook needle, a work support upon which a work piece having a thickconnected to the movable element, a flexible link connected to the spring and subjected by the spring to a variable force and means including a cam fixed to the rockshaft and over which the flexible .link passes, the cam providing a moment arm inversely proportional to the force to which the flexible link is subjected whereby a constant torque is applied to the rockshaft.

5. A shoe outsole sewing machine comprising a work support upon which a work piece having a thickness within a predetermined range is supported, a presser foot for gripping the work piece during a part of each sewing cycle, a curved hook needle for penetrating the work piece, a movable element connected to the presser foot, a presser foot lock for gripping and releasing the movable element during each sewing cycle, a rockshaft connected to the movable element, a torsion spring producing a torque output proportional to the thickness of a work piece within the range and compensating means for applying a relatively constant torque'to the rockshaft and through the movable element to give a relatively constant force to the presser foot regardless of work thickness including a flexible link one end of which is connected to the spring and a cam fixed to the rockshaft and to which the other end of the flexible link is connected and the periphery of which is engaged by the flexible link to apply the variable torque output of the spring through the link to the cam which provides a moment arm on the rockshaft inversely proportional to the torque of the spring.

References Cited by the Examiner UNITED STATES PATENTS 2,337,252 12/1943 Krag l12--6l 2,408,523 10/1946 Leveque 11261 2,600,424 6/1952 OLaughlin 112-61 FRANK I. COHEN, Primary Examiner.

P. D. LAWSON, Assistant Examiner. 

1. A SEWING MACHINE COMPRISING A CURVED HOOK NEEDLE, A WORK SUPPORT UPON WHICH A WORK PIECE HAVING A THICKNESS WITHIN A PREDETERMINED RANGE OF WORK THICKNESS IS SUPPORTED WHILE BEING PENETRATED BY THE NEEDLE, A PRESSER FOOT FOR GRIPPING THE WORK PIECE AGAINST THE WORK SUPPORT, A TORSION SPRING PRODUCING A TORQUE OUTPUT PROPORTIONAL TO WORK THICKNESS, A LOCK RELEASABLE DURING A PORTION OF EACH SEWING CYCLE FOR PERMITTING THE PRESSER FOOT TO BE URGED TOWARD THE WORK SUPPORT UNDER A FORCE FROM THE SPRING AND INTERCONNECTING MEANS FOR TRANSLATING THE TORQUE OUTPUT OF THE SPRING INTO A RELATIVELY CONSTANT FORCE APPLIED TO THE PRESSER FOOT THROUGHOUT THE RANGE OF WORK PIECE THICKNESS. 